O2451 POLYETHYLENE WEAR AND INSERT MICROMOTION IN RETRIEVED TOTAL KNEE REPLACEMENTS: DOES THE LOCKING MECHANISM DEGRADE WITH TIME?

Abstract

Aims: It has been suggested that the capture mechanism of modular polyethylene tibial inserts degrades with time in-situ. This study evaluates micromotion, polyethylene wear and tissue histology in contemporary cemented TKRñs retrieved at autopsy. Methods: Twelve cemented, PCL-retaining TKRñs of the same design were retrieved at autopsy after 41(15–74) months in-situ. Patient age and body weight averaged 73 years and 90 kg, respectively. Insert micromotion was measured according to published protocols on 6 of the 12 TKRñs in which the modular tibial component was undisturbed at retrieval and on 6 unused control components. Tissue histology was evaluated using a semi-quantitative grading system. Articular and backside surface damage was measured using published techniques. Results: There was no signiþcant difference (t-test, p=0.12) between the micro-motion index for retrieved inserts (154±121 um) and control inserts (62±53 um). Backside surface damage covered 38%±23% and was dimpled in appearance without scratching or pitting. Damage covered 46%±8% of the articular surface. Micromotion was negatively correlated with in-situ time (r=−0.94) and backside damage (r=− 0.97). Conclusions: Micromotion for these autopsy-retrieved TKRñs is less than half the 380 micron magnitude measured for other autopsy-retrieved designs, as reported by Engh. Micromotion was greatest on inserts with the least backside wear and the shortest time in-situ. These data suggest that backside damage resulted from axial compression of the polyethylene insert against the baseplate rather than micromotion.